The passive attack of the yellow mold stuns you for (level + 1)d4 turns. Its corpse is poisonous and hallucinogenic if eaten.

Strategy

If you lack the resistance required to neutralise the passive attack, it is best to let your pet attack the mold, attack it with a ranged weapon, or leave it alone. Molds will never move or actively attack you. If you let your pet take it out make sure they are strong enough to do so.

SLASH'EM

SLASH'EM features two new types of mold: the black mold and the disgusting mold. Their passive attack causes poison damage by way of spores; a nonbreathing character will be unaffected.

In both NetHack and SLASH'EM, the mold sometimes leaves a corpse. In SLASH'EM, the corpse might revive itself ("The yellow mold rises from the dead!"). Of little importance, when level drained, the draining persist between revivals, like with trolls. Also in SLASH'EM, molds may grow on rotting corpses.

In an old bug, molds growing on corpses, would take the name of the corpse if it was named. In practice this can be encountered if one is trying to play older patches.

Slash'EM Extended

Slash'EM Extended adds playable Mould and Ungenomold races, and while the player is in mould/ungenomold form, they have many disadvantages associated with being a fungus. The main disadvantage is the lack of limbs. However, these races also have uncurable polymorphitis, and being in ungenomold form is impossible since they genocide themselves right at the start of the game, forcing them to be polymorphed into a monster for the entire game (although they can change their form, they may never revert back to ungenomold). On the other hand, a mould character fully experiences the lack of limbs that prevents picking up items, putting on armor, opening/kicking doors etc.

Encyclopedia entry

Mold, multicellular organism of the division Fungi, typified
by plant bodies composed of a network of cottony filaments.
The colors of molds are due to spores borne on the filaments.
Most molds are saprophytes. Some species (e.g., penicillium)
are used in making cheese and antibiotics.